Solid tissue tumors, such as neoplasms of the liver, kidney, bone, adrenal gland, and brain, traditionally have been treated with systematic chemotherapy, surgical resection, or local radiation therapy. Many tumors, however, remain poorly responsive to these therapeutic modalities, thereby necessitating the use of alternative treatments, such as thermal ablation of the tumor. Thermal sources for these treatment modalities include high-intensity ultrasound, laser, microwave, and radiofrequency (RF) energy. Of these different types of ablation techniques, RF ablation has proven to be safe, predictable, and inexpensive, and has emerged as the thermal ablation modality that most easily creates large volumes of tissue necrosis.
Although RF ablation of the tumor can be implemented during open surgery, it is most often performed percutaneously. One RF ablation technique utilizes a single needle electrode or a multiple needle electrode array that is inserted percutaneously using a surgical probe and guided with real-time ultrasound, computed tomography (CT) imaging, or magnetic resonance imaging (MRI) into the tumor. Once properly positioned, the needle electrode is activated, and alternating current is transferred from the needle electrode into the surrounding tissue, causing ionic agitation of the surrounding cells, ultimately leading to the production of frictional heat. As tissue temperatures increase between 60-100° C., there is an instantaneous induction of irreversible cellular damage referred to as coagulation necrosis. The treatment area may be monitored ultrasonographically for increased echogenicity during the procedure, which corresponds to the formation of tissue and water vapor microbubbles from the heated tissue and is used to roughly estimate the boundaries of the treatment sphere.
Recently, a number of experimental and clinical studies have demonstrated the feasibility and safety of lung tumor ablation. However, some studies have shown limitations in achieving complete necrosis in large tumors measuring 3 cm or more in diameter. See Oshima et al., Lung Radiofrequency Ablation with and without Bronchial Occlusion: Experimental Study in Porcine Lungs,” Journal of Vascular and Interventional Radiology 2003, Vol. 15, No. 12. This is due, in large part, to the perfusion of blood through the lung tumor, which causes the conduction of thermal energy away from the target tissue and into the relatively cooler blood, thereby limiting the volume of the thermal lesion. In addition, a lung is composed of air spaces, and the air in the lungs is constantly flowing as a result of this ventilation. Thus, similar to effects of blood perfusion, the ventilation of air through lung tissue draws thermal energy away from the target tissue.
It is known to use a balloon to occlude a bronchial tube leading to the lung in which the target tissue is contained, which not only reduces the flow of air, but also reduces the perfusion of air, through the target tissue. A standard RF ablation probe can then be used to ablate the target tissue, which due to the reduced blood perfusion and air ventilation, creates a larger ablation lesion. While this procedure has been proven to be successful for ablating targeted lung tissue, it requires two separate devices (i.e., the occlusion catheter and the RF probe) with two different entry points (the patient's mouth and a percutaneous entry point through the patient's chest). As such, the complexity and invasiveness of such a procedure is increased.
For these reasons, it would be desirable to provide improved systems and methods for occluding the flow of fluid through a natural conduit within a patient's body, while delivering a therapeutic device via the natural conduit to a tissue treatment site to which the fluid would otherwise be supplied.